A phosphor is used in a vacuum-fluorescent display (VFD), a field emission display (FED) or a surface-conduction electron-emitter display (SED), a plasma display panel (PDP), a cathode-ray tube (CRT), a white light-emitting diode (LED), or the like. In any of these applications, in order to cause the phosphor to emit light, the phosphor should be supplied with energy for exciting the phosphor, so that the phosphor emits visible light by being excited by excitation light having high energy such as vacuum ultraviolet, ultraviolet, electron beams, and blue light. As a result of exposure of the phosphor to the excitation light, however, luminance of the phosphor tends to lower and deteriorate, and hence the phosphor less likely to experience lowering in luminance has been demanded. Accordingly, instead of conventional phosphors such as a silicate phosphor, a phosphate phosphor, an aluminate phosphor, and a sulfide phosphor, a sialon phosphor has been proposed as the phosphor less likely to experience lowering in luminance.
An exemplary sialon phosphor is manufactured with a manufacturing process as generally described in the following. Initially, silicon nitride (Si3N4), aluminum nitride (AlN), and europium oxide (Eu2O3) are mixed at a prescribed mol ratio, to fabricate a mixture. Then, the mixture is held in nitrogen at 1 atmosphere (0.1 MPa) at a temperature of 1700° C. for 1 hour and fired with hot pressing, to manufacture the sialon phosphor (see, for example, Japanese Patent Laying-Open No. 2002-363554 (Patent Document 1)). It has been reported that α sialon activated with Eu ions, that is obtained in this manufacturing process, serves as a phosphor emitting yellow light at 550 to 600 nm as a result of excitation with blue light at 450 to 500 nm.
In addition, a blue phosphor activated with Ce and including a JEM phase (LaAl(Si6-zAlz)N10-zAlz) as host crystals (see International Publication No. 2005/019376 (Patent Document 2)), a blue phosphor activated with Ce and including La3Si8N11O4 as host crystals (see Japanese Patent Laying-Open No. 2005-112922 (Patent Document 3)), and a red phosphor activated with Eu and including CaAlSiN3 as host crystals (see International Publication No. 2005/052087 (Patent Document 4)) have been known.
A phosphor in which a rare-earth element has been added to β-type sialon (see Japanese Patent Laying-Open No. 60-206889 (Patent Document 5)) has been known as another sialon phosphor, and it has been shown that a phosphor activated with Tb, Yb, and Ag serves as a phosphor emitting green light at 525 nm to 545 nm. A temperature for synthesizing the phosphor described in Patent Document 5, however, is as low as 1500° C., solution of an activating element in a solid state within crystals is not sufficient, and it remains in grain boundary phase. Thus, the phosphor achieving high luminance has not been obtained.
A phosphor in which divalent Eu has been added to β-type sialon (see Japanese Patent Laying-Open No. 2005-255895 (Patent Document 6)) has been known as a sialon phosphor emitting high-luminance fluorescence, and it has been shown that this phosphor serves as a green phosphor.
Here, unlike general illumination applications, a light-emitting device serving as a white light source used as a backlight source in a liquid crystal display or the like serving as an image display apparatus desirably has a narrow emission spectral line width of three primary colors of blue, green and red. The three primary colors are obtained as a result of transmission of white light through color filters transmitting only these respective colors. Here, green emission spectrum lying between blue emission spectrum and red emission spectrum is particularly required to be narrow in the emission spectral line width and to well match with the color filter for three primary colors.